The development of passive design features for the Korean Next Generation Reactor

Four passive design features, such as a fluidic device, a passive secondary condensing system (PSCS), a passive cavity flooding system, and a passive hydrogen ignitor, are under development as part of the Korean Next Generation Reactor (KNGR), an advanced PWR, to increase its safety. The fluidic device, which is located at the discharge of the safety injection tank, is a system to inject the borated water into the reactor coolant system in a passively regulating way to elongate the allowable start-up time of emergency diesel generators and to enhance performance against the loss of coolant accidents. The PSCS, which supplements the auxiliary feedwater system, secures the heat removal through steam generators in the case of the loss of feedwater event. The PSCS takes inlet flow from the steam line and returns condensate into the feedwater line after condensation through condenser tubes. Fusible plugs have been adopted for passive cavity flooding. If the ambient temperature is high enough, the plugs between the in-containment refueling water storage tank (IRWST) and the reactor cavity melt so that the IRWST water starts to flow into the reactor cavity by gravity. Passive hydrogen igniters (i.e. catalytic igniters) have been adopted in addition to the active hydrogen igniters to maintain containment hydrogen concentrations below a detectable limit of 10 volume percent. Applicability of these passive features on KNGR has been studied following the three-step approach of (1) preliminary analyses using computer codes and small-scale experimental facilities, (2) detailed analyses through large-scale tests, code running, and uncertainty validation, and (3) quality assurance by design verification and analyses on interfaces with other systems.